(1) Field of the Invention
This invention relates to a field emission type image display panel and a method of driving the same.
(2) Description of the Related Art
When the electric field at a surface of a metal or semiconductor is as large as 10.sup.9 V/m, electrons pass through the potential barrier because of the tunnel effect, thus emitting out in a vacuum at room temperatures. This phenomenon is called field emission. The cathode emitting electrons utilizing the principle is referred to as a field emission type cathode.
Recently, flat emission type field emission cathodes each formed of an array of micron-size field emission type cathodes (hereinafter, referred to as FEC) have been able to be manufactured fully using semiconductor machining technology.
The structure of a field emission cathode called a Spindt type cathode is schematically shown in FIGS. 13(a) and 13(b).
FIG. 13(a) is a perspective view showing a FEC fabricated using the semiconductor micromachining technology. FIG. 13(b) is a cross-sectional view showing the FEC, taken along the line A--A in FIG. 13(a).
Referring to FIGS. 13(a) and 13(b), a cathode electrode 102 is formed on the substrate 101 by using vapor deposition. Cone emitters 105 are formed on the cathode electrode 102. Gate electrodes 104 are formed over the cathode electrode 102 where the cone emitters 105 are not formed, via the insulating layer 103 of silicon dioxide (SiO.sub.2). The cone emitters 105 are respectively positioned in the round holes formed in the gate electrode 104 and the insulating layer 103.
That is, the tip of each cone emitter 105 is viewed in the hole opened in the gate electrode 104.
The cone emitters 105 are fabricated at pitch intervals of less than 10 microns, using micromachining technology. Thus, several ten to several 100 thousands of FECs can be fabricated on a single substrate 101.
Since the distance between the gate electrode 104 and the tip of the emitter 105 can be set in the order of submicrons, the emitter 105 can emit electrons caused by the field emission when a small voltage of several tens of volts is applied between the gate electrode 104 and the cathode electrode 102.
The above-mentioned FEC can be made as a flat field emission cathode. It has been proposed to apply the flat field emission cathode to a flat color display panel. The cross-section of the color image display panel is partially shown in FIG. 14.
In FIG. 14, columns of cathode electrodes 102 are arranged in a stripe from on the first substrate 101 of glass. Stripe-like gate electrodes 104 are arranged perpendicularly to the columns of the stripe-like cathode electrodes 102. The cone emitters 105 are arranged on the cathode electrodes 102 at the intersections.
The tips of the emitters 105 located at each of the intersections where the columns of the gate electrodes 104 intersects the columns of the cathode electrodes 102 point upward. The insulating layer 103 isolates the cathode electrodes 102 from the gate electrodes 104. Holes are formed in the insulating layer 103 to emit electrons.
The second substrate 110 of glass is arranged so as to confront the first substrate 101. A sheet of anode electrode 111 is formed on the nearly whole surface of the second substrate. Red fluorescent material 112, green fluorescent material 113, and blue fluorescent material 114 in stripe form are formed on the anode electrode 111 so as to confront the stripes of the cathode electrodes 102 respectively.
In order to display color images on the color display panel, the gate electrodes 104 are sequentially scanned and driven one by one while R, G, and B image data corresponding to one selected line of the gate electrode 104 are supplied to the cathode electrodes 102. Then, when all the gate electrodes 104 are sequentially scanned and selectively driven, a full color image for one frame is displayed on the second substrate 110.
However, in the color image display panel, it has been assumed that electrons emitted from the emitter 105 formed on the cathode electrode 102 reach the anode electrode 111, with a divergent angle of about 30.degree.. Hence, the problem is that electrons which reach the anode electrode 111 with a divergence of a considerable degree may glow a different color fluorescent material adjacent to the anode electrode 111. As a result, the color image displayed is blurred.
In order to solve the above-mentioned problem, the present applicant proposed a field emission type image display panel that can display color images with no blurring, by focusing electrons emitted from the emitter 105 (refer to the Japanese Patent Application (Tokugan-Hei) No. 7-114134).
FIG. 15 is a top view partially illustrating a field emission type image display panel proposed above.
In the field emission type image display panel of FIG. 15, stripe-like cathode electrodes 102 shown with chain lines are arranged on the first glass substrate (not shown). The cathode lead-out electrodes C1, C2, . . . , Cm are respectively connected to the stripe-like cathode electrodes 102.
Patch-like gate electrodes 120 are formed over the cathode electrodes 102 through an insulating layer (not shown) while they are arranged corresponding to respective pixels. As previously described, an emitter array is formed on the patch-like gate electrodes 120.
The second substrate (not shown) is arranged so as to confront the cathode electrodes 102. An anode electrode 111, shown with broken lines, is formed over the entire surface of the second substrate. R fluorescent, G fluorescent, and B fluorescent materials are formed on the anode electrode 111 so as to confront the respective patch-like gate electrodes 120. In FIG. 15, symbols associated with gate electrodes 120 represent colors emitted from the fluorescent material.
The patch-like gate electrodes 120 corresponding to G, B, and B pixels odd numbered in the (i) line (rows) are connected to the gate lead-out electrode GTi-1. The gate electrodes 120 corresponding to remaining R, G, and B pixels even numbered in the (i) line are connected to the gate lead-out electrode GTi.
Furthermore, the patch-like gate electrodes 120 corresponding to G, B, and R pixels odd-numbered of the (i+1) line is connected to the gate lead-out electrode GTi. The patch-like gate electrodes 120 corresponding to remaining R, G, and B pixels even-numbered of the (i-1) line is connected to the gate lead-out electrode GTi-1 (not shown). In a similar manner, in the gate lead-out electrodes GT1 to GTn, the patch-like gate electrodes 120 of an upper line (row) as well as the patch-like gate electrodes 120 of a lower line (row) are connected to each gate lead-out electrode in a zigzag pattern and every other gate electrode.
The gate lead-out electrodes GT1 to GTn are sequentially scanned and driven. For example, when the gate lead-out electrode GTi is scanned, the R, G, and B pixels even-numbered of the (i) line (hatched) and the G, B, and R pixels odd-numbered of the (i+1) line are driven.
When image data are correspondingly input to the cathode electrodes C1, C2, . . . , Cm respectively confronting the patch-like gate electrodes 120, an image can be displayed on the anode substrate. When the gate lead-out electrodes GTi-1 and GTi+1 not driven are set to a low level potential, preferably to the ground level, the adjacent patch-like gate electrodes 120 on the sides of each of the patch-like gate electrodes 120 (hatched) are driven to a low level potential. This allows electron beams emitted from the patch-like gate electrodes 120 driven to be focused.
As described above, in the field emission type image display panel using patch-like gate electrodes, electron beams emitted from the emitters 105 can be focused. However, in recent years, there have been strong demands for high brightness, high resolution, field emission type image display panels. It is required to more focus electrons emitted from the emitter 105.